1. Field of the Invention
The present invention provides a novel process for incorporating hydrophobic water-insoluble monomers which are solid at room temperature into acrylamide monomer solutions so as to permit the subsequent copolymerization of the monomers in the substantial absence of phase separation. In particular, the present invention is directed to a thermal process for incorporating alkyl acrylamides into an acrylamide monomer solution in the substantial absence of organic cosolvents.
2. Description of the Prior Art
Previous attempts at incorporating hydrophobic water-insoluble monomers into polymerizations to produce water-soluble polymers have entailed using various organic cosolvents to solubilize the hydrophobe. For instance, U.S. Pat. Nos. 3,919,140 and 3,969,329 disclose the use of about 15-30 percent by weight acetone in an acetone-water mixture to assist in the polymerization when hydrophobic monomers are added to an acrylamide polymerization. Similarly, U.S. Pat. No. 4,098,987 discloses the use of C.sub.1 to C.sub.4 alcohols, i.e., isopropanol, as cosolvents to disperse the hydrophobic monomers. In view of the ensuing chain transfer and reduction in molecular weight of the resultant polymer due to the large amount of cosolvent, there is need for improved methods of incorporating a hydrophobic monomer into a conventional water-soluble acrylamide polymer.
Alternatively, with the advent of water-in-oil emulsion polymerizations as means for preparing polyacrylamide emulsions, the addition of a hydrophobe has been accomplished by incorporating it into the oil phase; cf. U.S. Pat. Nos. 3,284,393, 3,624,019, 3,734,873, 4,152,307 and 4,452,940. However, in a solution polymerization there is no such oil phase available to provide solubility to the hydrophobe.
Finally, U.S. Ser. No. 904,908, filed Sept. 8, 1986, now abandoned, discloses a solution process for preparing hydrophobically functionalized cationic polymers. In this disclosure a water miscible cosolvent, i.e. acetone, methanol, isopropanol or mixtures thereof, is utilized to solubilize the water-insoluble monomer.